A stud bump bonding method that applies a conventional IC-related wire bonding technique to supersonically join golden bumps to those portions of a flip-chip IC in which an electrode is formed is well known and described below.
An example of a conventional bump bonding apparatus that is commonly used is shown in FIG. 4. A gold wire 1 is held by a damper 2 and penetrates a capillary 3. The capillary 3 is provided at the tip of a supersonic horn 4 provided on a supporting frame 5 that can rotationally move around the horizontal axis. When the supporting frame 5 is rotationally moved by a head vertical driving apparatus 6, the capillary 3 is moved in the vertical direction via the supersonic horn 4. The head vertical driving apparatus 6 comprises a coil motor. In addition, a supersonic oscillator 7 is provided on the supersonic horn 4.
The supporting frame 5 is provided on a horizontal moving table 8 that can move in the X and Y directions that cross each other in a horizontal plane. When the moving table 8 is moved, the capillary 3 moves in the horizontal direction. In addition, reference numeral 9 is a displacement detection sensor that detects the vertical displacement of the supporting frame 5, and the vertical position of the capillary 3 is determined based on the displacement of the supporting frame 5 detected by the displacement detection sensor 9.
An air tensioner 10 that lifts the gold wire 1 is provided above the clamper 2. In addition, a heat stage 12 that supports and heats an IC 11 is provided below the capillary 3. A heater 13 is provided in the heat stage 12. A spark generating apparatus 14 is provided near the tip of the gold wire 1 that is inserted through the capillary 3. A position-recognizing camera apparatus 15 for recognizing the position of the IC 11 is provided above the heat stage 12.
According to this configuration, the position-recognizing camera apparatus 15 recognizes the IC 11 on the heat stage 12 for positioning. Then, as shown in FIG. 5a, the spark generating apparatus 14 applies sparks to the tip of the gold wire 1 protruding downward from the capillary 3 in order to form a gold ball 16.
Subsequently, the head vertical driving apparatus 6 lowers the capillary 3, as shown in FIG. 5b. When the gold ball 16 abuts a portion of the IC 11 in which an electrode is formed from above, the vertical displacement of the supporting frame 5, which is detected by the displacement detection sensor 9, stops at a constant value to allow the height position of the electrode forming portion of the IC 11 to be detected. A predetermined amount of pressure is applied to the capillary 3 to press the gold ball 16 downward, and the supersonic oscillator 7 oscillates supersonic waves via the supersonic horn 4 to join the gold ball 16 to the electrode forming portion of the IC 11. This operation allows a bump pedestal 17 to be formed in the electrode forming portion of the IC 11.
Then, as shown in FIG. 5c, the capillary 3 is elevated a specified amount by the head vertical driving apparatus 6 and then moved in the horizontal direction a specified amount by the movement of the moving table 8, followed by lowering.
Then, as shown in FIG. 5d, the gold wire 1 abuts the bump pedestal 17 from above. The head vertical driving means is a VCM (voice coil motor) which allows the displacement detection sensor 9 to detect displacement while the value of driving current is measured. The current value increases at the time of abutment, but there occurs no more displacement. When the current exceeds a certain value (threshold value), it is so judged that the gold wire 1 has abutted the bump pedestal 17, and displacement at that time is stored. A predetermined amount of pressure is then applied to the capillary 3 to press the gold wire 1 downward to join it to the bump pedestal 17.
Then, as shown in FIG. 5e, the capillary 3 is again elevated a specified amount by the head vertical driving apparatus 6. The gold wire 1 is then raised by the air tensioner 10 while it is held by the damper 2, thereby causing the joint between the gold wire 1 and the bump pedestal 17 to be broken to form a protruding stud bump 18 in the electrode forming portion of the IC 11, as shown in FIG. 5f.
Such a conventional technique has the following problems.
FIG. 6 shows the stud bump 18 that is normally shaped. According to the conventional technique, however, in forming the stud bump 18, if, in the step shown in FIG. 5d, the position at which the bump pedestal 17 is formed is offset in a direction that leaves the capillary 3 in the horizontal direction (that is, to the left of the normal forming position as shown by imaginary line A in FIG. 7), the position at which the bump pedestal 17 and gold wire 1 are joined together becomes lower than the normal position. If the position at which the bump pedestal 17 is formed is offset in a direction that approaches the capillary 3 in the horizontal direction (that is, to the right of the normal forming position as shown by imaginary line B in FIG. 7), the position at which the bump pedestal 17 and gold wire 1 are joined together becomes higher than the normal position.
Thus, if the forming position of the bump pedestal 17 is offset in the horizontal direction to vary the height of the joining position between the bump pedestal 17 and the gold wire 1, the stud bump 18 may be inappropriately shaped; for example, it may be destroyed while the gold wire 1 on the stud bump 18 side is standing in the vertical direction as shown in FIG. 8 or while the gold wire 1 on the stud bump 18 side is released from the bump pedestal 17. Such an inappropriate shape of the stud bump 18 causes the electrode to be connected inappropriately, thereby causing an inappropriate IC 11 to be produced.
In addition, the electrode forming position of the IC 11 and the position of the bump pedestal 17 are detected when the displacement detected by the displacement detection sensor 9 stops at a constant value. The search time required for detection, however, is relatively long and two detections (that is, the detection of the position of the electrode forming portion of the IC 11 in FIG. 5b and the detection of the position of the bump pedestal 17 in FIG. 5d) are required to form a single stud bump 18, resulting in a long production tact.
It is an object of this invention to provide a bump bonding method and apparatus that prevents bumps from being shaped inappropriately and that reduces the time required to form bumps.